stores a version of this code, with minor corrections, as a
self-contained snippet (for historical purposes mainly), both
on the LSR (as an upgrade to snippet #102) and in a dedicated
subsection of the Snippets doc page.

as a result, chord-generic-names.scm is no longer found in scm/
and the chord-names-jazz.ly doc chart no longer includes any
alternative chord naming systems (that were already broken anyway).

chordNamesExceptionsFull and chordNamesExceptionsPartial
properties have been removed as well (both having no longer had
any effect whatsoever for quite some time).

the main (and now only) chordNamesExceptions property def
has been slightly updated for slightly neater glyphs and spacing,
and so as to now include power chords by default; as a result,
\powerChords is no longer needed, thereby solving any possible
confusion with \germanChords and the like. (I can’t think of any
case where users would explicitely type \chords{c:5} in order to
get the same output as \chords{c} -- can you?)

the documentation has been updated as well; convert rules
have been added (although these may be merged with previous
2.21.0 rules once the release cycle gets back on track).